Body, generic

B0851 Right Brake Lamp Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Published J2012 tables skip B0851, and service literature and NHTSA filings never cite it either. The title names the right stop-lamp circuit. The GM-developed Saab 9-3 tests this lamp whenever the brake light is on and stores B3878 04 once the right lamp draws less than 50 mA; the high-mounted lamp is judged separately under B3884 with a lower limit of 20 mA. If both sides and the third lamp go dark together, the cause usually lies upstream, at the brake light switch or a shared fuse, not in one lamp circuit. For today's networked rear lamps HELLA names failed LED segments and faulty plugs as typical findings. FMVSS 108 requires working stop lamps on every car. Repair without delay; left side: B0850.

Likely causes

Right stop-lamp bulb or LED segment failed
Loose or corroded plug at the right tail lamp
Wire to the right tail lamp broken
Lamp driver in the rear module faulty

Symptoms

  • Right brake light dark while the left one and the third lamp work
  • Brake light warning in the display
  • Reduced braking signal to following drivers; repair at once

Repair estimate

DifficultyEasyDIY possible
Parts and labour€5–300
Time0.2–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

right brake lampbody control module

Related codes

B0850B0235

References: saabwisonline.com, saabwisonline.com, hella.com, law.cornell.edu.